The invention relates to devices for propagating magnetic domains. Such devices each include a monocrystalline nonmagnetic substrate bearing a layer of an iron garnet. The iron garnet is capable of supporting local enclosed magnetic domains, and it has a uniaxial magnetic anisotropy induced substantially by growth on the nonmagnetic substrate. The iron-garnet is of the class of iron garnet materials in which at each dodecahedral site there is at least a large ion and a small ion.
In magnetic "bubble" domain devices, that the smaller the bubble diameter, the larger the information storage density which can be achieved. Iron garnet bubble domain materials are preferred for use in bubble domain technology because small diameter bubble domains are stable in these materials. For a bubble domain material to be useful for the manufacture of bubble domain devices, it is important that the bubbles formed in the material should have a high wall mobility so that comparatively small driving fields can cause rapid bubble movement. This property permits use of high frequencies with low energy dissipation.
It is also important that magnetic bubble domain materials should have a high uniaxial anisotropy. This is necessary to avoid spontaneous nucleation of bubbles. This is of great importance for reliable information storage and processing within the bubble domain material.
The overall uniaxial anisotropy (K.sub.u) may have stress or strain induced components (K.sub.u.sup.s) and may have growth-induced components (K.sub.u.sup.s). This means that EQU K.sub.u .apprxeq.K.sub.u.sup.s +K.sub.u.sup.g ( 1)
In the usual bubble domain materials, K.sub.u is mainly determined by the growth-induced component. In choosing ions to occupy dodecahedral sites in the lattice of a bubble garnet material (in order to increase the growth-induced anisotropy), in the past the choice was restricted to magnetic rare-earth ions. This was because the accepted theory for growth-induced anisotropy required the use of magnetic ions. However, the magnetic rare-earth ions used in the past provided additional damping, so that these choices did not lead to an optimum domain mobility. In fact the smaller the bubble domain becomes, the more damping ions have to be incorporated to reach the required high uniaxial anisotropy.
Netherlands Patent application No. 7514832 (see, also, U.S. Pat. No. 3,995,093) discloses a bubble domain device in which there is lanthanum and lutetium in the dodecahedral sites of the bubble domain material so as to produce the high bubble domain wall mobility which is desirable for operation at high frequencies. A film of this known material proves to have a growth-induced uniaxial anisotropy (K.sub.u.sup.g) of 6800 erg/cm.sup.3, which is only sufficient to produce stable device behavior with a bubble domain cross-section not smaller than 4 .mu.m.
The high growth-induced uniaxial anisotropy (K.sub.u.sup.g) of films of this known material is attributed to the combination of lanthanum (the largest of the rare-earth ions) with lutetium (the smallest of the rare-earth ions). The high bubble domain wall mobility is a result of the fact that neither lanthanum nor lutetium contribute to the damping except to a small extent. However, a disadvantage of this material is that only a small amount of lanthanum can be incorporated in the garnet lattice. Consequently, the anisotropy resulting from the combination of a large rare-earth ion and a small rare-earth ion at the dodecahedral lattice sites cannot be optimized.